1. Field of the Invention
This invention relates to manufacturing methods, and more particularly, to an apparatus and a method for indication of the operational status of equipment used in semiconductor fabrication.
2. Description of the Relevant Art
Fabrication of integrated circuits upon semiconductor substrates (xe2x80x9cwafersxe2x80x9d) involves numerous pieces of equipment (xe2x80x9ctoolsxe2x80x9d), processing steps, and personnel. Wafer fabrication technicians (WFTs) are responsible, in part, for preparing wafers and processing wafers on various tools. Maintenance technicians"" duties include maintaining and repairing tools. Tool manufacturer (xe2x80x9cvendorxe2x80x9d) representatives may be present for evaluating and correcting problems with one or more tools. Engineers determine the required processing steps, a tool to be used for each processing step, and processing parameters to be used by the tool while performing that step. Managers may be responsible for overseeing a portion or all of the fabrication processing steps and coordinating the efforts of personnel associated with those steps. Efficient fabrication requires good communication between all personnel associated with the fabrication process.
A tool may have one of several operational statuses. For example, a tool may have an xe2x80x9cupxe2x80x9d, xe2x80x9cdownxe2x80x9d, or xe2x80x9cqualificationxe2x80x9d status. A tool with an up status is available to be used for processing wafers. A tool with a down status cannot be used for processing wafers. The tool may have the down status if a problem with the operation of the tool is discovered and corrective action is being taken. The tool may also be given the down status during regularly scheduled preventative maintenance. A tool with a qualification status cannot be used for processing product wafers, which are wafers upon which functional circuits are being fabricated. One or more test wafers, however, may be processed by the tool having the qualification status. Test wafers, which are wafers that do not have functional circuits being fabricated upon them, are typically processed using only a single tool for the purpose of assessing the performance of that tool. The tool may be given the qualification status during routinely scheduled checks of the tool""s performance. The tool may also be given the qualification status after corrective action or after preventative maintenance has been performed on the tool having the down status.
Some of the tools used in semiconductor fabrication have multiple chambers within which wafers are processed. Each chamber of these tools may have its own individual operational status. For instance, one chamber may be broken and therefore have a down status while the remaining chambers are in good working order and have up statuses. For multiple-chambered tools, the operational status of the tool refers to the operational status of every chamber of the tool.
Semiconductor fabrication is typically performed in clean rooms. These are special areas in which the quantity of particles in the air is kept extremely low by continually flowing air from the ceiling to the floor and by ensuring the equipment and people in the clean room generate as few particles as possible. This is necessary since any particle that adheres to the surface of a wafer may destroy the integrated circuit being fabricated upon that portion of the wafer. Any device brought into the clean room must be essentially free of particles and further the operation of any device within the clean room must not generate large quantities of particles.
Each tool used in semiconductor fabrication is generally controlled by its own computer. Typically such a computer has one or more terminals next to the tool it controls. Each of these terminals usually consists of a monitor for sending output to a tool user and one or more input devices for the user. An automated factory system is often used to control the flow of wafers among tools and to ensure that the correct processing parameters are used for each wafer. This system is typically connected to the computers controlling the individual tools and this system may also maintain a database of the operational status of each tool. An example of an automated factory system is WorkStream(trademark) sold by Consilium, Inc. of Mountain View, Calif.
It is important that all personnel associated with a tool are kept informed of the tool""s operational status. Typically, two different forms of communication are used. The first form involves maintaining a record of the operational status of a tool in a computer database, typically the automated factory system. Personnel can find out the operational status of a given tool by logging onto the automated factory system and reading the operational status off the appropriate screen. The second form of communication is verbal. When a person changes the operational status of a tool, that person can then tell other personnel the tool""s new operational status. Additionally, when personnel working with the tool are changed, such as during a shift change, the departing personnel can inform the arriving personnel of the current operational status of a tool.
Several problems can occur with these two forms of indicating the operational statuses of tools. Typically, a WFT is responsible for processing wafers on multiple tools in addition to other duties such as preparing wafers for processing. Preparing wafers for processing may include sorting wafers and performing pre- and post-processing measurement of the wafers. A tool with a down status may be repaired and given an up status by a maintenance technician while the WFT responsible for processing wafers on that tool is performing other duties at a different location. In this case, the maintenance technician will change the status of the tool in the automated factory system; however, since the WFT is not currently present, the maintenance technician cannot inform the WFT verbally of the change in operational status. If the WFT does not have occasion to check the operational status of the tool in the automated factory system, the WFT will not realize the tool is available for use. Hours may elapse before the WFT becomes aware that the tool can be used to process wafers. This idle time of the tool results in lost productivity and increased manufacturing costs.
During shift changes, the departing WFT has to inform the arriving WFT of the operational status of every tool for which he is responsible. Since a single WFT is often responsible for processing wafers on multiple tools, of which one or more of these tools may have multiple chambers, the WFT is required to remember the operational status of every tool in addition to other assignments the WFT may have. If the WFT forgets the operational status of a tool, he or she will have to stop what he is doing to check on the operational status in the automated factory system.
High-level managers may visit the fabrication area to check on the quality of the work being performed. Idle tools represent significant loss of productivity and increase of manufacturing costs. If a manager sees a tool not being currently used, he or she may find the WFT responsible for processing wafers on that tool and require the WFT to explain why the tool is idle. This takes time away from the WFT""s duties and decreases his or her efficiency even though the tool may be currently idle for good reason. For example, the tool may have a qualification status, a test wafer may have recently been run on the tool, and the WFT is currently waiting on an assessment of that test wafer.
Tools may also be scheduled to be temporarily removed from production. For instance, a tool may be given a down status for regularly scheduled maintenance or a tool may be given a qualification status for a regularly scheduled check of the tool""s performance. In these instances, the WFT that is processing wafers on a tool may be unaware that the tool will be taken out of production at a specific time. If the WFT had a reminder that the tool was to be taken out of production, the WFT could adjust the processing of wafers to ensure that the wafers of highest priority are processed before the tool is removed from production.
It is therefore desirable to develop a supplemental form of indicating the operational status of a tool that would allow any personnel working in the vicinity of a tool to easily determine its operational status. It is also desirable if some form of a warning about a scheduled change in the operational status of a tool could be given. It is further desirable that any additional indication of the tool""s operational status be coordinated with the tool""s status as recorded in the automated factory system to avoid any confusion about the actual status of the tool.
The problems outlined above are in large part addressed by an apparatus that continuously indicates the operational status of the tool to which it is attached. Such an apparatus allows any personnel in the vicinity of the tool to determine the operational status of the tool by looking at (or listening to) the apparatus. Since the apparatus is attached to the tool, any change of the tool""s operational status can be quickly noticed. For instance, if a maintenance technician places a tool in the up status after making repairs and cannot find the WFT to inform him that the repairs are complete, the WFT will notice the change in operational status the next time the he is in the vicinity of the tool. Additionally, any other personnel, such as a manager, can walk past the tool and determine its operational status without having to interrupt the work of others to inquire about the tool""s status.
In one embodiment, the apparatus is a mechanical sign that displays in color and/or words the operational status of the tool. The sign is preferably attached to the front of the tool and is constructed of materials that are compatible with the semiconductor fabrication environment. The sign may be formed such that it includes a separate section for indicating each operational status of the tool. For example, there may by three sections, one each for the up status, the down status, and the qualification status. Each section may contain the words, xe2x80x9cupxe2x80x9d, xe2x80x9cdownxe2x80x9d, or xe2x80x9cqualificationxe2x80x9d, as appropriate. Additionally, the up section may be colored green, the qualification section may be colored yellow, and the down section may be colored red. To denote the current operational status, covers may be used to hide the other two status indication sections. If the tool contains multiple chambers, the sign preferably comprises sections for indicating each possible operational status for each chamber.
In a preferred embodiment, the mechanical sign comprises labels for each of the sections held between two pieces of clear, static-free Lexan(trademark). The continual air flow present in the clean rooms where semiconductor fabrication occurs tends to cause insulating surfaces to acquire an electrical charge. The use of static-free Lexan(trademark) in the construction of the sign prevents this charging from occurring. Lexan(trademark) is manufactured by the General Electric Company of Schenectady, N.Y. The covers are preferably made from opaque, static-free Lexan(trademark) and are attached to the sign by Teflon(trademark) roller bearings held captive in grooves located on the sign. The covers can be moved by hand to allow the appropriate operational statuses to be covered. The use of Teflon(trademark) bearings reduce the quantity of particles that may be generated when the covers are moved. Teflon(trademark) is made by the E. I. du Pont de Nemours and Company of Wilmington, Del. Additionally, the grooves may also contain notches to retain the cover directly in front of one of the operational status indications. An advantage of a mechanical sign is that it requires no electrical connections and contains very few parts that could break or malfunction. The mechanical sign should therefore last the lifetime of the tool to which it is attached and will most likely never fail and require repair.
To ensure that the operational status indicated by the sign agrees with the operational status recorded by the automated system, a video camera may be used to check the operational status indicated by the sign. The video camera may be taught the location of the sign and can determine the operational status indicated by the sign by determining which color is displayed by the sign. This indication can then be compared to the operational status recorded by the automated system. If disagreement is found, a warning can be generated to inform the appropriate personnel of the discrepancy.
In another embodiment, the apparatus is a set of lights or audible signals corresponding to the possible operational statuses of the tool. The current operational status is indicated by illuminating the appropriate light or activating the appropriate signal. For example, the lights may indicate the operational statuses by color and/or words. For example, there may be three lights, one each for the up, down, and qualification statuses. The words, xe2x80x9cupxe2x80x9d, xe2x80x9cdownxe2x80x9d, and xe2x80x9cqualificationxe2x80x9d may be written on or near the lights. Additionally, the light may be colored green to indicate the up status, red to indicate the down status, and yellow to indicate the qualification status. If the tool contains multiple chambers, the apparatus preferably comprises a set of lights for the possible operational statuses for each chamber.
In one embodiment, personnel such as WFTs or maintenance technicians may manually illuminate the appropriate light by activating a switch placed near the light. In a preferred embodiment, the lights are an integral part of the tool and the illumination of the lights is controlled by the computer that controls the tool. The computer would read the operational status of the tool from the automated work system. The computer could then send signals that would cause the appropriate light to be illuminated. This would guarantee that the operational status recorded by the automated factory system would agree with the operational status displayed by the lights.
A method for indicating the operational status of a tool is also contemplated herein. The method includes changing the status of the tool recorded by the automated factory system. A computer that controls the tool is linked to the automated factory system. The automated factory system then downloads the new operational status to the computer. The computer then causes the new operational status of the tool to be indicated. The operational status may be indicated by a set of lights as discussed above or the operational status may be displayed upon a monitor that comprises an output terminal of the computer. The operational status is preferably displayed as words upon the monitor.
The method further contemplates indicating any scheduled changes of the operational status of the tool. For instance, if the tool is scheduled to be placed in the down status for preventative maintenance, this may be indicated at some time prior to the tool actually being placed in the down status. Scheduled changes in the operational status are recorded in the automated factory system. At some time prior to the scheduled change, for example two hours beforehand, the automated factory system can download this information to the computer that controls the tool. The computer can then indicate that the scheduled change is to occur by flashing the appropriate light or by flashing the appropriate operational status on the monitor. By warning personnel of the impending change in operational status, they can ensure that they are ready for the change in status when it occurs. For instance, if the tool is being placed in the down status for preventative maintenance, the appropriate personnel can ready themselves so that they can begin work as soon as the tool is given the down status. This will minimize the time the tool is in the down status and that in turn increases manufacturing efficiency and reduces manufacturing costs.